Sitting near Phoenix right now. My concern about running the fan is when the compressor cycles off, the room air is being circulated through the duct in the ceiling and up through the AC unit then back into the room. I?m thinking there is probably cooling loss. (I?m sure every rig is different, if the air coming out of the ducts seems really warm when the compressor isn?t running I?d probably not run the fan continuously.) On the other hand, allowing the unit to run on low fan automatically, means the compressor will run longer. Hard to say. What I?m doing is letting it cycle until the heat gets to be enough that it seems like the compressor is running most of the time, then I switch the fan to high.